The invention is directed to a noise damper or silencer for pipelines carrying noise-laden gasses, particularly for an intake line and/or exhaust gas line of an internal combustion motor. The damper comprises an outside pipe with an admission side and a discharge side, a plurality of diaphragm rings having a respective outside surface in communication with the inside surface of the outside pipe and at least one insert having an outside surface in communication with either the inside surface of the outside pipe and/or of the diaphragm rings. The insert has a plurality of openings closed at one side, and the insert forms sub-lines or passages for the gas flow in the noise damper. The openings closed at one side open into the sub-lines and have a depth of xcex/4 with reference to the wavelength xcex of a frequency to be damped.
A fundamental distinction is made between three types of damper that are based on different physical principles, namely:
1. Absorption noise dampers
What is expected of an absorption noise damper is that higher, especially bothersome frequencies are absorbed, sucked up by absorption materials or, respectively, converted into frictional heat.
EP 0 834 011 B1, for example, discloses an absorption noise damper for an internal combustion motor composed of an intake pipe carrying the intake air and of a resonator housing that surrounds the former upon formation of a closed resonance space. In addition, the absorption sound damper is equipped with an admission muff and a discharge muff, and has openings in the pipe wall of the intake pipe that connect the interior of the intake pipe to the interior of the resonator. A chamber wall of an axial sequence of a plurality of chamber walls directed transverse relative to the longitudinal axis of the intake pipe thereby forms or, respectively, form resonator chambers of different volume in the resonator housing that are hermetically limited from one another, so that each resonator chamber communicates with the interior of the intake pipe via openings in the pipe wall of the intake pipe without bridging chamber walls, and comprises a mutually matched dimensioning of the resonator chamber volume, of the cross-sectional area of the opening and of the thickness of the intake pipe in the region of the respective opening corresponding to the wall height of the openings for each individual resonator chamber at the position and width if a resonator frequency band that is respectively structurally prescribed therefor. Each opening and the appertaining resonator chamber therefore respectively form a Helmholtz resonator tuned to the frequency band to be absored, i.e. to be damped.
2. Reflection sound dampers
The function of reflection sound dampers is based both on reflection of sound waves as well as on reflection of sound waves to the acoustic source and on multiplication of sound points. The damping is thereby all the more effective when the reflection locations are more numerous.
For example, WO 97/09 527 discloses a reflection sound damper for gas-carrying pipelines having an admission, a discharge and a chamber lying between these connections in the air intake tract of an internal combustion motor, links or diaphragms that re duce the flow cross-section of the chamber being arranged in said chamber transverse to the flow direction.
3. Interference sound dampers
In interference sound dampers, a part of the acoustic energy is extinguished when merged after covering paths of different length.
Many combinations of the sound damper types recited above are, of course, known in the Prior Art. For example, DE 197 03 414 A1, which defines the species, discloses a specific combination of sound damping mechanisms. This discloses a combination of a reflection sound damper in the form of diaphragm rings connected axially following one another and a resonance damper in the form of xcex/4 resonators. The high flow losses due to the diaphragm rings are disadvantageous in the known noise damper; moreover, there is still not a satisfactory tunability of the frequencies to be damped, neither in view of the range nor the broadband quality.
The invention is therefore based on the object of developing the noise damper of the species to the effect that the disadvantages of the Prior Art are overcome, and a tunable damping is possible particularly in the frequency range from 1 through 20 kHz.
The present object of the invention is achieved by at least one apertured wall that extends between at least two diaphragm rings with an outside surface in communication with at least the inside surface of the two diaphragm rings, so that at least one resonance chamber is defined between the two diaphragm rings, the apertured wall and the outside pipe.
It can be provided that the insert comprises essentially plate-shaped inside walls that are provided on both sides with blind holes or openings closed at one side. The inserts are arranged essentially cross-shaped or star-shaped in a radial cross-section and preferably extend over essentially the entire axial length of the outside pipe.
It is also proposed that the blind holes or openings closed at one side are arranged offset relative to one another on both sides of an inside wall.
It is also provided that the openings closed on one side are arranged essentially in rows from the admission side to the discharge side, whereby the depth of the openings closed on one side is the same within a row and different from row to row, preferably with increasing depth from the admission side to the discharge side.
It is also inventively proposed that the distance between the diaphragm rings differs, preferably increasing from the admission side to the discharge side.
A preferred embodiment of the invention is characterized in that at least one resonance chamber and at least one hole in the apertured wall of the resonance chamber form a Helmholtz resonator that can be tuned to a frequency band to be damped via the volume of the resonance chamber, the cross-sectional area of the hole in the apertured wall of the resonance chamber and the wall thickness of the apertured wall of the resonance chamber in the region of the hole.
It can thereby be provided that the wall thickness of the apertured wall amounts to 0.6 through 5 mm, and is preferably 1 through 3 mm.
It is also proposed that one or more apertured walls arranged following one another from the admission side to the discharge side extends or, respectively, extend over the entire axial length of the outside pipe, and preferably concentrically within the outside pipe.
It is also preferred that a plurality of resonance chambers are provided, whereby frequency bands to be damped by neighboring resonance chambers preferably at least partially overlap and/or the resonance chambers form reflection sound dampers and/or absorption sound dampers.
It can also be provided that the diaphragm rings are provided with blind holes or openings closed at one side that open into the sub-lines or passages